A.V.D Bica

The use of hall effect semiconductors in geotechnical instrumentation

For the past five years or so Hall effect semiconductors have been increasingly used in the geotechnical engineering laboratories at the University of Surrey. They have been incorporated as sensing elements in local radial and axial strain measuring devices, for the small-strain instrumentation of triaxial specimens, and in small diameter boundary normal and shear stress cells. Triaxial internal load cells are currently being built incorporating Hall effect semiconductors. This paper describes the Hall effect principle and the methods of configuring magnet/sensor systems to achieve suitable measuring systems. Some geotechnical instruments built at the University of Surrey are detailed, and their characteristics discussed. The calibrations of the instruments described in the paper show a performance generally at least as good as might be expected from some commercially available instruments. Hall effect semiconductors are shown to be of use in a range of situations where displacement can form the basis of measurement. The displacements measured can vary from as little as 5 µm to as much as 10 mm, and the best repeatability so far obtained has been of the order of 1/100 of a micrometre.

Hall effect instrumentation for stress and force measurements

Instruments for the measurement of normal stress, shear stress and force in geotechnical engineering laboratory applications are described. These instruments are similar in design to existing strain-gauged instruments, but instead make use of linear output Hall effect sensors. The basis of measurement in all cases is displacement rather than strain. The performance of each instrument is assessed, and it is shown that Hall effect sensors can readily be incorporated in such a way as to produce acceptable levels of accuracy.

Tension pile tests in chalk

This paper reports the results of a series of pull-out tests performed on mini-piles in chalk. Also reported are load–displacement data for similar piles when used in a group, for anchoring large-diameter plate loading test equipment. A comparison is made with the limited data reported in the literature. The observed uplift resistance of these piles is compared with that predicted by existing design methods, based upon SPT, and vertical effective stress.

DISCUSSION. LIMIT EQUILIBRIUM DESIGN METHODS FOR FREE EMBEDDED CANTILEVER WALLS IN GRANULAR MATERIALS.

This Paper is fairly restricted in its subject matter, but, as will be discussed later, there areimplications which are common to most formsof geotechnical design. 49. The subject of the Paper is restricted to a simple wall type (Fig. 1) embedded in granular soil...